1. Field of the Invention
The present invention is in the field of electrical power production from steam flashed from high temperature geothermal brines which have a high content of dissolved silica, and also a content of hazardous classified constitutents.
2. Description of the Prior Art
Some high temperature geothermal brine resources are known which contain very large amounts of geothermal energy, but which until recent years had not been usable for the commercial production of electrical power because of a high dissolved silica content. Thus, in the Imperial Valley of California, the Salton Sea Known Geothermal Resources Area (KGRA), otherwise known as the Salton Sea Geothermal Anomaly, is estimated to have approximately 3,400 MW.sub.e of geothermal energy available for the generating of electrical power, which is believed to be self-regenerating by percolating waters. The KGRA geothermal resource is estimated to be a greater energy reserve even than the oil reserves on the North Slope of Alaska. A similar geothermal resource is the Brawley geothermal field which is also in the Imperial Valley of California. Development of these large geothermal reources was almost completely blocked until recent years by the high dissolved silica content, which precipitated out on walls of vessels and piping in power production plants to the extent of up to about 42 inches thickness per year of scaling. This problem was resolved by Magma Power Company, now of La Jolla, San Diego County, Calif., by flashing the geothermal brine to steam for generating electrical power in a series of first high pressure and then low pressure flash crystallizers in which the dissolved silica was precipitated out on a vast silica seed particle area rather than on surfaces of flash vessels and asociated piping and valves. The use of flash crystallizers for this purpose was first taught in the Featherstone U.S. Pat. No. 4,429,535, while retrieval in reactor clarifiers of the silica seed particles useful for the purpose was taught in the VanNote U.S. Pat. Nos. 4,302,328 and 4,304,666.
In geothermal electrical power plants embodying the flash crystallizer/reactor clarifier technology for preferentially precipitating out the silica on silica seed particles suspended in the geothermal brine flowing through the plant in flash crystallizers, and then retrieving the preciptated particulate silica in reactor clarifiers, there is a huge output quantity of precipitated silica sludge that is removed from the reactor clarifiers and then thickened and pressed into filter cake for disposal and/or use as a filler material in concrete or for other purposes. A serious problem with this now conventional procedure is that there is still some precipitation which grows on walls of vessels and pipes in the plant which tends to break loose in particulate form and join the silica particles in the geothermal brine flowing through the plant, and thus become intermingled with the particulate silica in the silica sludge retrieved from the reactor clarifiers, so as to become a part of the silica sludge filter cake that must be disposed of. The problem here is that such intermingled scale particles contain a number of substances classified as hazardous materials, including but not limited to arsenic, lead, copper, zinc and silver. Prior to the present invention, this conventional silica retrieval procedure has prevented or seriously restricted the disposal of the silica filter cake as simple landfill in sanitary refuse disposal areas, thus making the disposal undesirably complicated and expensive; and it also has made the use of this filter cake plant byproduct in concrete or for other purposes undesirable or possibly even unlawful.